Analysis of Product Structural Design: The common sealing methods employed in high-temperature thermal oil rotary joints primarily fall into two categories: flat-face sealing and spherical sealing. Among these, the spherical sealing structure is the most prevalent; it achieves a seal by utilizing the mutual compressive contact between spherical surfaces (a concave sphere and a convex sphere). The advantages of rotary joints utilizing this method include automatic seal adjustment, lower requirements for equipment concentricity, the use of dual oil-free bearings, and a maintenance-free design. However, their disadvantages include relatively high frictional resistance and lower permissible rotational speeds. To compensate for wear, this design employs springs to axially displace the housing, allowing it to follow the sealing surface; this mechanism typically requires a relatively large range of axial movement (swing space).
Spherical-seal rotary joints are prone to several issues: scratching of the rotating shaft's sealing surface; spring fatigue or thermal deformation of sealing components caused by sudden temperature fluctuations; seizing of support or guide rings; leakage at the main seal interface; and-due to the constraints imposed by inlet and outlet hose connections-restricted axial movement of the housing, which can lead to accumulated tolerance errors, causing misalignment (wobble) and subsequent leakage. This structural design represents one of the most common types of rotary joints currently in use.
Analysis of Sealing Pairs and Material Selection: The main seal is the critical component of a rotary joint; the selection and pairing of sealing materials directly determine the quality of the joint. Currently, domestic manufacturers of thermal oil rotary joints widely utilize carbon-graphite materials for their sealing rings. These soft carbon-graphite rings are typically paired with hard metal structural components; the surface hardness of the metal counterpart must be controlled within a reasonable range to ensure optimal performance when paired with high-quality carbon-graphite rings.
Naturally, depending on specific operating conditions, many manufacturers also employ alternative materials-such as cemented carbide, silicon carbide, silicon nitride, aluminum oxide, copper alloys, and filled PTFE-for their sealing rings. Furthermore, the selected materials must be compatible with the specific working medium. Applications requiring resistance to acids or alkalis necessitate surface anti-corrosion treatments, while high-temperature applications require the use of heat-resistant materials.